Several small-animal reflectance optical imaging systems are offered commercially for qualitative observations of surface fluorescence in tissues. However, no commercial small animal or clinical imaging system that enables quantification of fluorochromes in highly scattering media such as biological tissue exists. The overall goal of the current proposal is to develop and refine the tools, algorithms and system designs necessary to develop a commercial small animal imaging system capable of performing volumetric and quantitative measurements of exogenous tissue fluorescence in vivo. Such quantification will be critical for accurately assessing the expression of molecular targets in diseased tissues and evaluating the pharmaceutical efficacy of drugs. The development of a small animal imaging system is expected to lay the foundation for the future development of a clinical fluorescence imaging system. This proposal truly represents a unique opportunity to develop novel technologies for in vivo imaging. Importantly, since VisEn is developing both the fluorescent imaging agents and systems, the Company is in an ideal position to concurrently optimize both imaging probe and system technologies to truly advance the field of optical molecular imaging. The specific goals of this Phase I grant proposal are: 1. Design and implement advanced illumination schemes for multi-angle transillumination 2. Develop appropriate theoretical models for the illumination scheme 3. Test and validate the illumination scheme and theoretical models using phantoms and in vivo 4. Prepare for Phase II studies